A significant issue in the maintenance and upkeep of known gas turbine engines is the creation of lubricating oil varnish. For example, lubricating oil in a hydraulic circuit may be in communication with a number of servos that operate inlet guide vanes, gas control valves, liquid fuel valves, etc. Varnish deposits on the oil wetted components and elsewhere may lead to the failure and/or the malfunction of these servos and other components. Such failures and malfunctions may result in the tripping of the gas turbine engine and a subsequent revenue loss caused by the downtime for required repairs.
Oil varnishing may be the result of a complex string of events. Specifically, the molecules in the oil stream may be broken via chemical, mechanical, and/or thermal processes. For example, chemical processes may include oxidation of the oil. Oxidation may be accelerated by heat and/or the presence of metal particulates therein. Mechanical processes may include “shearing,” where the oil molecules may be torn apart as they pass between moving mechanical surfaces. Thermal processes may include pressure-induced dieseling or pressure-induced thermal degradation due to the high pressures and temperatures. Electrostatic charges also may cause localized thermal-oxidative oil degradation. Turbines that are operated in a peaking or a cycling mode may be more susceptible to oil varnishing due to the effects of thermal cycling. Other processes and combinations thereof also may be present although not fully understood to date.
There is thus a desire for oil varnish mitigation systems so as to limit both the creation of oil varnish and the damage caused thereby, particularly in a hydraulic circuit with the servos therein and other components that may be susceptible to varnish damage and the like. Reducing varnish damage should improve overall system efficiency and reduce required maintenance and downtime. Such varnish mitigation systems may be retrofitted into existing gas turbine engines or may be original equipment in new systems.